Low cost cathode ray tube (CRT) data displays typically utilize standard television receiver circuitry which employs tightly tuned "high Q" deflection circuits and low video bandwidth for noise rejection. The imperfect interlacing experienced in such low cost receivers cause undesirable line pairing and interline flicker. The resulting display is so degraded seen at an arm's length distance, that it becomes necessary to limit use of the horizontal display lines to one-half of the 525 lines of the CRT raster, thus significantly reducing the resolution of the display.
Standard television circuitry has a 4.2 megaHertz bandwidth, a 15.75 kiloHertz line rate and a 10.2 microsecond retrace interval which limits the number of dots which may be displayed to 448 dots per line for cathode ray systems employed for data display purposes. In applications where compatibility of the display system with Hollerith type punch card inputs is desired, for a minimum 80 character per line display the capability of the above-mentioned system limits each character to a maximum of 5 dots per row, in order to stay beneath the maximum 448 dots permitted per line.
Although standard television type receivers are relatively inexpensive, efforts to modify such devices for purposes of producing data displays of high quality have nevertheless resulted in significant cost increases. Design techniques utilized to obtain improved performance have been so specialized as to lead to the development of special purpose monitors which unfortunately have limited areas of application.
The need for high quality information displays and the ability to provide a high quality display in compact low-cost systems having low power requirements dictate the need for a totally new design approach. The growth in need for displays to present computer outputs of 132 characters per line, for example, and for displaying the fine print in legal documents, typesetting apparatus and the like require display systems operating at significantly higher bandwidth and line frequency which requirements are not capable of being achieved in systems of the type described hereinabove, especially with the constraints of compact size, low power and low cost.